The present invention relates a plasma processing apparatus and more particularly, to a plasma processing method suitable for performing a surface treatment of a semiconductor substrate and the like by using plasma.
In recent years, a semiconductor device has been miniaturized and thus, an etching process for transferring a mask formed by lithography to an underlying film is required to have higher dimensional accuracy, that is, higher CD (Critical Dimension). In the mass-production field, in addition to the high CD controllability, assurance of the reproducibility of CD is of an important problem. Generally, accounted for causes of a change in the CD are the deposition of a reaction product generated from a material being processed on the inner wall of an etching chamber, the consumption of members inside the chamber attributable to their long-term use and the change in temperature and the like factor of the members inside the chamber followed by a change in the probability of deposition of a radical on the inner wall of the chamber and the like, leading to the eventual change in a plasma affecting the etching performance.
Further, in a miniaturized transistor, the capacity of a gate insulation film needs to be increased in order to control the short channel effect and conventionally, this problem is solved by decreasing the thickness of a gate oxide film. With the thickness of the gate oxide film reduced, however, a leakage current increases and hence, a material having a higher dielectric constant (High-k) has been introduced for use as the gate insulation film. As the High-k material substituting for the oxide film, a hafnium oxide film (HfO2) can be enumerated. But, because there is an unfit of material between the conventional poly-silicon (Poly-Si) electrode and the hafnium oxide film (HfO2), a structure having a metal film of a proper work function is needed. Of various kinds of the metal material enumerated, TiN and La have been used as described in Semiconductor International Vol. 2008/1 (Non-Patent Document 1).
Conventionally, in the plasma processing apparatus, cleaning based on plasma is performed wafer by wafer or lot by lot and for processes targeting a carbon (C), an oxide film, Poly-Si and a nitriding film, cleaning to be executed in a plasma principally containing either fluorine (F), chlorine (Cl) or oxygen (O) or a mixture of any of them has been used. In the event that the inner wall member of the etching chamber is consumed to generate a metal or the like (for example, Al) which in turn is deposited on the interior of the chamber, removal of the deposited metal is difficult to achieve through cleaning based on plasma only and therefore, a technique has been studied in which the atmosphere inside the chamber can be kept constant in advance or preparatorily by using seasoning, for example. As an example of this type of technique, a technique described in JP-A-2004-031380 (Patent Document 1) has been known.
Also, a technique described in U.S. Pat. No. 7,204,913 (Patent Document 2) has been known according to which coating is applied to the inner wall of a reactor each time that a wafer process proceeds with the aim of decreasing an influence the change in status of the reactor inner wall has upon the process performance.
On the other hand, as described in Journal of Vacuum Science and Technology B24, 2191 (2006) (Non-Patent Document 2), it has been known that when a metal material (for example, TiN) is etched, the metal is deposited on the chamber inner wall and complete cleaning will sometimes be difficult to achieve in the gas system.